As well known to those skilled in the art, rubber boats are designed such that they expand to form predetermined shapes when being inflated with compressed air, and float in the water due to buoyancy exerted by the water in which the inflated boat bodies are immersed. Such rubber boats are easy to carry and store out of use, so they are widely and preferably used as leisure boats and rescue boats.
However, the rubber boats are made of rubber which is easily cut or torn, so the inflated boat bodies of the rubber boats are often seriously damaged upon impact during a voyage or colliding against sharp edges or sharp points when being at anchor in the harbor. Therefore, such rubber boats sometimes present safety hazards resulting in loss of lives in the case of careless management of them. The rubber boats are thus inferior in terms of safety, and force persons boarding the boats to carefully manage the boats, thus being inconvenient to the persons during a voyage or while being at anchor in the harbor.
Another problem of the rubber boat resides in that the boat bodies are made of soft rubber, so the boats cannot offer stability or comfort to persons boarding the boats. The rubber boats also experience severe frictional resistance from water during a voyage, thereby undesirably reducing mileage in the case of motorboats.
In an effort to provide a boat that overcomes the above-mentioned disadvantages experienced in the conventional rubber boats in addition to retaining the advantages of the rubber boats, the inventor of the present invention proposed a prefabricated boat that consists of a boat body formed of reinforced plastics, with rubber tubes attached along both sides of the plastic boat body to increase buoyancy of the body, in Korean Patent Application No. 98-14548.
FIG. 9 is an exploded perspective view of the above-mentioned prefabricated boat. In the prefabricated boat, the front part 11 of the deck 13 of a boat body 10 made of reinforced plastic group synthetic resins is projected laterally outward along each side edge, thus enlarging contact surfaces between the rubber tubes 20 and the body 10. Upper and lower tube locking recesses 30, each consisting of a fitting inlet end 32 and a longitudinal groove 31, are formed along the upper and lower portions of each sidewall 12 of the boat body 10 in such a way that the inlet end 32 of the lower locking recess is positioned in back of the front part 11. The rubber tubes 20 each have upper and lower slidable fittings 21 at positions corresponding to the upper and lower locking recesses 30 of each sidewall 12 of the boat body 10. Therefore, the rubber tubes 20 are thus detachably attached to both sides of the boat body 10 through a detachable engagement of the tubes' fittings 21 with the body's locking recesses 30. Each of the above rubber tubes 20 has a longitudinal cylindrical shape, and is streamlined at its front portion to create a typical projectile shape, and is attached along each side of the boat body 10 such that the pointed front end of the rubber tube 20 is directed toward the front part 11 of the boat body 10.
Therefore, the prefabricated boat with rubber tubes enlarges the size of the boat body's front part 11, to which frictional resistance exerted by the water is concentrated during a voyage. The boat thus minimizes possibility of damage to rubber tubes which cannot effectively endure frictional impact due to intrinsic properties of rubber, and attenuates the rolling of the boat body, different from conventional boats made of boards, so the boat gives stability and comfort to persons boarding the boat as well as improving safety during a voyage. However, the conventional prefabricated boat having rubber tubes has several problems as follows.
First, when the rubber tubes are attached to both sides of the boat body through a detachable engagement of the tubes' fittings with the boat body's locking recesses, most parts of the tubes except for the fittings are directly exposed to the outside of both sides of the boat body, so the surface contact areas between the tubes and both sidewalls of the boat body are limited to the fittings of the tubes. Therefore, when hydraulic frictional resistance is continuously exerted to the rubber tubes by the water during a voyage of the boat, hydraulic impact caused by the frictional resistance repeatedly stresses the areas of the tubes around the fittings, thus quickly damaging the tubes.
Second, the prefabricated boat does not have any means for absorbing and dispersing impact energy caused by the hydraulic frictional resistance exerted to the tubes by the water, so persons aboard the boat suffer from severe pitching of the boat body during a voyage. The boat is thus degraded in its sailing stability and cruising power, as well as its mileage.